Yet with each erratic and violent outburst, North Korea is fueling a debate in ruling circles in Beijing over how far China should go in backing the regime in Pyongyang. Over time, those in China who argue that strategic economic interests should take precedence over security ones, thus tipping China more toward South Korea and the West, could lead to an erosion of its reflexive support for Pyongyang. Beijing is not there yet, though.

"China uses its leverage cautiously because it wants to keep the DPRK [Democratic People's Republic of Korea] stable," says Cai Jian, deputy head of the Koreas Research Center at Shanghai's Fudan University. "If the pressure were too strong, it might lead to the country's rapid collapse."

The world is watching closely to see what Beijing's response will be to North Korea's latest provocation, the shelling of a South Korean island in late November. China remains North Korea's only solid international ally – and a powerful one. For years Beijing has tolerated its neighbor's mercurial and often dangerous behavior, keeping the country afloat with fuel and food, protecting it from tough United Nations sanctions, and keeping it diplomatically engaged with the United States.

'China's spoiled child'

North Korea may be a "spoiled child," as a frustrated top Chinese diplomat told a US official according to a State Department cable published by WikiLeaks, but it is China's spoiled child.

There is no doubt that "China is the single most influential country over North Korea," says Denny Roy, a North Korea expert at the East-West Center in Hawaii. Its potential leverage is such that Beijing could sink the North Korean government at will by cutting off vital supplies.

But it likely won't do that. Experts note that however embarrassing Beijing finds Pyongyang's actions – such as testing two nuclear devices, sinking a South Korean naval vessel earlier this year, and the recent artillery shelling of Yeonpyeong Island that killed four people – North Korea's stability remains paramount. "China's No. 1 goal is to prevent a collapse of the [North Korean] regime," says Dr. Roy.

At the same time, Beijing finds North Korea – a country that emerged from the Korean War nearly 60 years ago – a useful counterweight to one of Washington's closest allies in the region, South Korea. As long as North Korea maintains a formidable military establishment, the Chinese can be sure that no potential enemy will try to overrun North Korea, as would have happened in the Korean War but for China's intervention. In a real sense, North Korea's military establishment is a front line of defense for the Chinese.

Keeping the balance

"China is close to the DPRK not because we love its system, but because we just want to keep the balance on the Korean Peninsula," says Dr. Cai. That leaves Beijing "not a lot of choice" but to maintain its support for Pyongyang, he adds.

Signs are growing, though, that China is losing patience with its errant ward. Beijing joined the rest of the world in condemning North Korea's second nuclear test last year, which was a direct affront to the Chinese government. China chairs the Six-Party Talks, a currently moribund diplomatic effort to denuclearize North Korea also involving the US, Russia, Japan, and South Korea.

And in an intriguing snippet from the latest WikiLeaks revelations, the US ambassador in Seoul reported a conversation with a South Korean vice minister who said that two senior Chinese officials had told him informally that Beijing would not object to a reunification of Korea under Seoul's government.

Undoubtedly, Beijing's strategic economic interests lie with South Korea, Japan, and the US rather than with North Korea, and "there was a serious debate in [the] Chinese Foreign Ministry and academic circles" last year about whether to maintain China's support for North Korean leader Kim Jong-il, says Cai. The security-minded hardliners won that debate, however, he says.

Regime change in North Korea could lead to daunting short-term problems for China, such as the threat of a flood of refugees. It would also mean "longer-term uncertainty about what a united Korea would mean strategically for China," Roy points out, and represent a betrayal of the ideological bond and sense of obligation that older Chinese leaders feel for the authorities in Pyongyang. "That package of disadvantages weighs heavily enough that China is prepared to tolerate even the kind of behavior we have seen recently," says Roy.